1. Field of the Invention (Technical Field)
The present invention relates generally to the field of hovering and vertical take off and landing vehicles. More specifically, the present invention relates to air-vehicles with ducted fans as the propulsion system.
2. Background Art
Ducted fan configurations are known for their superior aerodynamic performance over non-ducted fans and several implementations of ducted fan hovering air-vehicles have been developed and flown. However, most of these vehicles either utilized single duct configurations with the engine center mounted or utilized rotating ducts attached to a fuselage to for thrust vectoring.
Hovering vehicles utilizing a single ducted fan configuration have the engine mounted either in a puller or pusher arrangement in the inlet or exit of the duct flow. Engine mounting is to the duct ring. Stator assemblies are implemented just after the fan to remove the induced fan swirl to provide linear axial flow. Thrust vectoring is accomplished with sets of vanes in the resulting exit airflow. Avionics and payloads are either mounted inline with the engine (forward or aft of the fan/stator assembly) or as pods on the outside surface of the duct.
The problem is that the physics of the various parameters of; packing size weight and volume, endurance, acoustics, and fuel consumption all play against each other to make an optimum system that is humanly portable by the average soldier. The objective is to provide a vertical take off and landing and hovering vehicle with the greatest payload carrying capability and longest endurance and yet fit within the portable packing constraints of a soldier's equipment carrying system. This requires a critical balance of the vehicle payload, performance, endurance or persistence, propulsion system, control system, and weight, while minimizing acoustic signature.
The application of ducted fan propulsion to hovering air-vehicles has been attempted and successfully demonstrated in various configurations but successfully meeting all the needs for a deployable system requires a combination of utility and physics of the problem to be addressed. These hovering air-vehicles utilize well known physics of mass properties that generate thrust from moving air, that direct the air to control attitude, and axially linearize the air flow removing induced swirl for added thrust. Human back packing ability imposes additional weight, container constraint sizing constraints and plays against performance and set up times with a resulting reduced payload and endurance. Solutions that apply single ducted fans with inline engines exhibit reduced fan and duct efficiencies arising from engine, engine mount avionics, payload, and vane airflow disturbances. These single ducted fan solutions also suffer from increased aero-acoustic noise signatures because of these same airflow disturbances. The trailing attitude control vanes impact not only the acoustic noise signature but contribute to added drag and do nothing to counteract the natural outflow contraction ratio.
Managing the center of gravity along the duct axial direction and laterally across the duct is critical to making the vehicle controllable. Payload modularity is severely limited for axial locations with payloads of varying mass distributions as small shifts of the cg require control stabilization changes and can very quickly make the vehicle uncontrollable. Laterally located payloads are also often used but the mass properties require that there be a close to even balance between opposing masses relative to the axial axis of the fan. These vehicles are statically unstable and even though passive stability is desired it is not attained. Compounding the cg management problem is the electrical wiring between pods and control effectors. There are no convenient wire routing channels between payloads and avionics located around the exterior of the duct or axially above or below the engine. The compromises will usually impact weight, efficiency, and limit payload modularity.
Centrally mounted engines impact structural integrity of the payload pod mounting and the engine mount structure. Minimum gap between the fan blades and the duct is desired for greatest efficiency but is limited by the engine vibration and structural bending of the engine mound and duct. The duct attachment point is also a high structural failure point. Sensor integrity is compromised when blurred by vibration from payload pods mounted cantilevered around the duct and in front of or below the engine due to natural body bending modes. These effects add up to more exotic materials and weight to manage the undesirable effects.
Endurance and/or persistence of the vehicle mission are impacted with the limited fuel carrying capacities when the only location for fuel is limited to the interior of the duct.
Sensor visibility is severely restricted by either axially in-line or laterally duct mounted pods. Vehicle orientation in forward flight will obscure an axially down looking sensor mounted below the fan. Vehicle orientation in hover will obscure an axially mounted sensor above the engine. Laterally mounted side pod sensors have good visibility forward and down in hover and forward flight, but are limited to side viewing.
Structurally integrated systems that require close tolerances and layered assemblies limit the fielded utility of a potentially back packable system through increased setup and teardown times. Specialized tools may be required to remove assemblies and higher skill levels are required. Maintenance, repair, and replacement of components is limited because of the complexity associated with component assembly.
With all these issues previous solutions have focused only on individual elements of the problem or some combination of the problems but have failed to provide a solution that addresses the complete physics of a fieldable system. A system that combines the performance of larger duct sizes, enhances the duct aerodynamic efficiency, is inaudible to the human ear, supports a variety of payload sizes weights mass distributions and electrical interfaces, is reconfigureable for missions, provides high structural solidarity for maximum sensor utility, supports backpacking for human transport, and provides rapid setup tear down and maintenance actions is provided in this invention.
The following are prior art patents that disclose differing types of prior art inventions that are lacking the inventive concepts of the present invention. U.S. Pat. No. 6,691,949, entitled Vertical Takeoff and Landing Aerial Vehicle; U.S. Pat. No. 6,672,538, entitled Transmission for a Coaxial Counter Rotating Rotor System; U.S. Pat. No. 6,655,631, entitled Personal Hoverplane with Four Tiltmotor; U.S. Pat. No. 6,607,162, entitled Ring-Wing Aircraft; U.S. Pat. No. 6,270,038, entitled Unmanned Aerial Vehicle with Counter-Rotating Ducted Rotors and Shrouded Pusher-Prop; U.S. Pat. No. 6,170,778, entitled Method of Reducing a Nose-Up Pitching Moment on a Ducted Unmanned Aerial Vehicle; U.S. Pat. No. 6,065,718, entitled Universal VTOL Power and Rotor System Module; U.S. Pat. No. 5,941,478, entitled STOL/VTOL Free Wing Aircraft with Modular Wing and Tail; U.S. Pat. No. 5,890,441, entitled Horizontal and Vertical Take Off and Landing Unmanned Aerial Vehicle; U.S. Pat. No. 5,863,013 and U.S. Pat. No. 5,575,438, entitled Unmanned VTOL Ground Surveillance Vehicle; U.S. Pat. No. 5,419,513, entitled Ancillary Aerodynamic Structures for an Unmanned Aerial Vehicle Having Ducted, Coaxial Counter-Rotating Rotors; U.S. Pat. No. 5,407,150, entitled Thrust Unit for VTOL Aircraft; U.S. Pat. No. 5,372,337, entitled Unmanned Aerial Aircraft Having a Single Engine with Dual Jet Exhausts; U.S. Pat. No. 5,351,913, entitled Coaxial Transmission/Center Hub Subassembly for a Rotor Assembly Having Ducted, Coaxial Counter-Rotating Rotors; U.S. Pat. No. 5,277,380, entitled Toroidal Fuselage Structure for Unmanned Aerial Vehicles Having Ducted, Coaxial, Counter-Rotating Rotors; U.S. Pat. No. 5,226,350, entitled Drive Train Assembly for a Rotor Assembly Having Ducted, Coaxial Counter-Rotating Rotors; U.S. Pat. No. 5,150,857, entitled Shroud Geometry for Unmanned Aerial Vehicles; and U.S. Pat. No. 5,145,129, entitled Unmanned Boom/Canard Propeller V/STAL Aircraft.